Stop tipping. I mean it. Don't give extra money if you don't feel like it. Tipping is not mandatory in Spain or in most of the European countries. You can leave some coins if you feel like it, or the spare change they bring you after paying the check, but waiters don't expect it -- they have their salaries and tips are extra money for them -- not what they live on.
Therefore, tourists in the States, coming from the other bay of the Atlantic Ocean, are amazed when dining out. And not because of the delicious food or the huge portions (serving size deserve a post by itself), but because of the tips they feel the need to pay: 20 percent to be polite and if everything was satisfactory. Less means you're not happy with the waiter. No tip means you might be in trouble and you better run.
The opposite works similarly: American tourists in my country give tips as if they are in the US. Restaurateurs are delighted with their kindness and how they generously radiate money, so they chase them up and down La Rambla (or any other attractive spot in big cities all over Europe) because tourists equal good money.
Some may say that if waiters have almost non-existing salaries and need to make tips in order to earn some money by the end of the day, they will do their best to keep their customers happy. But in fact, "tip" is the acronym for "To Insure Proper Service," thus it's the money you give to the workers to make sure next time you'll have the same pleasant treatment you had this time. But the reality is different: some waiters swarm around the tables they serve, pushing the customers to consume more just so their tip is bigger. And it's annoying for all who are involved.
Seeing a large group of tourists in the States eating dinner makes you feel like grabbing a chair and ordering some popcorn. Plus, it's cheaper than the movies. Unless it's a family and the parent pays for the entire meal, the show begins: on top of the check they need to add the taxes and the tip, 20 percent and never less for groups like this, then split the amount and cross their fingers for the waiter to accept their need to pay separate. What was originally supposed to be a quiet evening turns out to be a cranky one.
So who's the winner in this 'tipping game?' The owner, of course. He pays loose change to his employees and lets the customers pay for their job. Instead, everyone should have a decent salary, and let the tips be an extra bonus, a reward, but just if their job was remarkable. In the U.S., it's illegal for government workers to receive tips, and there's a reason for it. Tipping and bribing are not that different.